Photoacoustic systems for measuring the thicknesses and adhesion properties of metal and opaque films in a film stack on a substrate are well known. An optical generator and detector of stress pulses useful in such photoacoustic systems in disclosed in U.S. Pat. No. 4,710,030 to Tauc et al. A schematic diagram of one arrangement of an optical stress-pulse generation and detection system 34 is shown in FIG. 1. The system 34 includes radiation source 36 for providing pulsed pump beam PM and radiation source 38 for providing a continuous probe beam PB. The wavelength of the pump beam PM is selected so that it is strongly absorbed in the particular film to be studied or in a medium associated with the film.
Pump beam PM and probe beam PB are directed to film 40 through lens 42. Mirrors 44, 46 and 48, 50 direct pump beam PM and probe beam PB, respectively, to lens 42. The portion of pump beam PM that is not absorbed by film 40 is reflected as ray 52 and prevented from reaching photodector 54 by beam-blocker 56. When the induced stress pulse returns to the surface of film 40 it causes a slight variation in reflectivity which changes the intensity of reflected ray 58 of continuous probe beam PB. The photodector 54 has a sufficiently short response time to respond to the fast changes in reflectivity. The output of detector 54 is displayed in sampling oscilloscope 60 as a function of time. Signal averager 62, interfaced with oscilloscope 60, integrates the responses over many pump beam pulses and improves the signal-to-noise ratio. Examples of other optical stress pulse generation and detection systems for photoacoustic systems for measuring thin film are disclosed in the patent to Tauc et al.
An example of an implementation of the photoacoustic measurement technology of the Tauc et al. patent in an automated metrology system 51 useful for measuring thicknesses of metal films on wafers by semiconductor manufacturers is shown in the block diagram of FIG. 2. The metrology system 51 includes measurement stage 61, robotics and wafer handling system 65, measurement system 75, cassette station 70, computer controller 55, and communication lines 80. Computer controller (controller) 55 is electrically connected to measurement system 75, measurement stage 61, robotics and wafer handling system 65, and cassette station 70 via communication lines 80. Controller 55 further includes software embodied in a computer-readable medium capable of carrying out the steps of the measurement method.
In a typical operation, controller 55 sends an instruction to the robotics and wafer handling system 65 to extract a wafer from cassette station 70, and to position the wafer on the measurement stage 61. The controller 55 then issues commands to the measurement stage 61 to position the wafer relative to the measurement system so that measurements can be made at a predetermined location. The measurement stage includes a test surface upon which the wafer is placed for measurements and translation stages to provide wafer manipulation in three degrees of freedom. The controller 55 then issues commands to the measurement system 75 to make a measurement and display the results of the measurement. Once the measurement is complete, controller 55 issues instructions to the robotics and wafers handling system 65 to return the wafer to the cassette station 70.
The assignee of the present application, Rudolph Technologies, Inc., manufacturers automated metrology systems which operate in accordance with the system 51 shown in block diagram in FIG. 2. These systems are marketed under assignee's registered trademark MetaPULSE, and are particularly useful by semiconductor manufacturers as film thickness metrology tools for 200 mm and 300 mm wafers.
The automation platform of the known automated metrology systems is shown in FIG. 3. As depicted in FIG. 3, the metrology system 51 comprises a single measurement tool or metrology 90 in which the measurement stage 61 and measurement system 75, FIG. 3, are located. The robotics and wafer handling system 65 and cassette station 70 are located in a front end 91 of the system. Electronics unit 92 contains the computer controller 55. A front opening unified pod (FOUP) 93 is used with the system to protect and transport wafers having films to be measured.
There is a continuous, strong desire by semiconductors manufacturers to find ways to increase their rate of production and, at the same time, to lower their production costs. There is a need for an improved automated metrology system which would do both.